The present invention relates to a network adapter for connecting a local area network to a backbone network and, more particularly, to a network adapter comprising an address transformation table in which are registered pairs each consisting of a node address and a local area network address, indicating a local area network to which a node assigned with the node address belongs.
In a network system in which local area networks (to be hereinafter referred to as a LAN or LANs) are connected to a backbone network via network adapters, each network adapter receives data (frame data) concerning a LAN connected to itself. A destination node address is set in a destination address field of the frame data concerning the LAN, and a source node address is set in its source address field. If a destination node indicated by the received frame data is present in the connected LAN (intra-LAN), the network adapter discards the received frame data; otherwise, it generates frame data destined for another LAN to which the destination node is connected, and transmits the frame data onto the backbone network. A destination LAN address is set in a destination address field of the frame data concerning the backbone network, a source LAN address is set in its source address field, and frame data received from the LAN is set in its data field.
The frame data on the backbone network is received by a network adapter corresponding to a LAN indicated by the destination address field of this data. When the network adapter receives the frame data on the backbone network, it sends a data field portion of the frame data to a LAN connected to itself. The data concerning the LAN is received by a destination node indicated by the destination address field of this data.
The above is a description of the operation by which data is transferred among LANs, through the backbone network of the network system connecting some LANs thereto.
In the above network system, each network adapter connected to the backbone network must recognize the connection relationship among LANs, nodes, and their node addresses. In a conventional system, address pairs each consisting of a node address and a LAN address are provided for each network adapter, as hardware data or data in a non-volatile memory.
However, with this conventional system, each time a node is either added to or omitted from a LAN, or is exchanged for another type, the system operation is interrupted, and the hardware data, as well as data in the non-volatile memory, must be rewritten in all the network adapters.